Most prior art surface grinding machines are hydraulically powered and are dedicated to a specific grinding function such as creep feed grinding, shortstroke grinding, or pendulum grinding. Presently, there exists no one machine which can perform all of these grinding functions without alteration or replacement of parts thereof. As a result, if a user must perform each of these different grinds on a workpiece, three different machines are required, and the workpiece must be moved from machine to machine to perform the desired grinds in the desired sequence. Such an operation can be extremely time consuming, and it is very expensive to have to maintain several different machines.
Existing machines used for pendulum type grinding at speeds of about 1200 inches per minute or greater generally use a hydraulic system as a primary drive for the table carrying the workpiece. Although a hydraulic drive is sufficient for pendulum type grinding, it is unacceptable for creep feed grinding at speeds in the range of ten inches per minute, or less. For such slower speeds, a separate and dedicated machine is required, generally having a steel band or steel cable drive or a ball screw nut drive, or a rack and pinion drive.
In addition, such existing grinding machines are subject to errors and must be carefully monitored to perform the high precision grinds required for modern applications. In particular, most such machines have a first set of ways upon which the table containing the workpiece travels. A second set of ways perpendicular to the first set of ways is provided for travel of a column containing the grinding wheel and the wheel housing assembly. Generally, the base supporting the first set of ways is formed separately from the base supporting the second set of ways, and the two bases are affixed to one another by conventional welding or bolting techniques. As a result, if the two bases are not precisely assembled, misalignment can occur, resulting in grinding errors. In addition, use over a period of time can produce a slight misalignment of the bases. A two-base construction also tends to be elastic in the vertical and horizontal plane, thus contributing to errors in precision grinding. In prior art machines, both the first and the second set of ways generally extend beyond their suporting bases and are insufficiently supported at their ends. This insufficient support can result in errors in grinding because of flexing of the ways during the operation of the machine and because of machine induced vibrations. The hydraulic reservoir and all of the hydraulic apparatus for prior art pendulum type grinding primary drives are generally disposed within the base beneath the first set of ways. The hydraulic reservoir and apparatus generate a considerable amount of heat, and regardless of the precautions taken, thermal gradients result in the first set of ways and the table. These gradients can produce distortion or misalignment of the ways and table, which may produce errors in the grinding operation. Also, hydraulic drives are subject to other problems, such as leaks, inefficiency and require filtration and/or heat exchangers.
Some existing machines, especially creep feed grinding machines, use a threaded shaft and a ball screw nut arrangement for the primary drive. Such a drive is subject to weave as the shaft is rotated because of stresses on the shaft and because of minor imperfections in the threading. In addition, heat generated by the interaction of the shaft and the nut is transferred to the table and ways, also possibly producing errors in the grinding operation. In order to produce the precision grinds desired, the column containing the wheel housing must be maintained in a precisely vertical orientation and must frequently be aligned prior to use to assure precision grinding.
During periods of power interruption or permanent power cut-off, the weight of the grinding wheel tends to carry it downwardly into the workpiece. Such movement as the grinding wheel is dropping down can cause irreparable damage to the work piece. In order to prevent such damage, conventional grinders utilize counterweights or pneumatic or hydraulic systems to maintain the wheel head position during power interruption. Such prior art devices are often clumsy, inefficient, require external power sources, and do not act instantaneously.
Most prior art surface grinders are manually operated and controlled, utilizing hand-held wheels. These wheels are not always ideally positioned for grinding operations, and must be continually monitored by the operator to assure precision grinding. In addition, only one grind along one axis may be performed at any one time, and if a grind on a second or third axis is desired, this must be performed in a separate operation.